For the questions: how to spread the bacteria- I have always added the bacteria and phage to the semisolid and plated that way and it worked great, of course do not add when the semisolid is too hot or you get nothing. Either way should work fine its just what your comfortable with.

Do not store dilutions overnight because your titer will probably drop at least a log. My best advice for working with phage is do everything fresh and take everything out of freezer or wherever as soon as you need it even if you have to wait for things to thaw.

As for your other questions, those will most likely be better answered by someone who works with the particular phage as different phage like different conditions, but maybe you can look on the ATCC website or email someone from tech support or something?

First to say that I never worked with Listeria phages, but here are my thoughts:

You might try to enrich your phages by growing them simultaneously with bacteria. Ie, when you put an an overnight culture to grow - put different amounts of phages (from your ATCC stock) in the culture too. That way, tomorrow you should have them in higher amounts in your supernatant. You can then use the supertnatant as a source of phages. I make 0.75% agar, melt it, add both phages and bacteria (fresh overnight), and pour it on a plate but over a thin layer of normal nutrient broth medium (M17 with glucose for Listeria, right?). 

I would be surprised if good titer drops significantly in such a short while, such as overnight. Of course, you should use SM buffer, not saline for storage of your phages.

You should of course consult ATCC if you don't solve the problem...

I think the key poit is do you observe phage plaque or phage zone on bacterial lawn? If yes, I think it is very easy to get high concentration. I am working with several phage infecting bacteria from marine environment, not related to your phage, but i have some idea for you: 

How to grow the phage to maximize them? We've tried concentrating a 48hr liquid culture of bacteria and then incubating with phage for another 48 hours. This still doesn't seem to have worked.

It is not good, because MOI very important for phage infection. You may be not know how the phage titer you got, so you dont know MOI. Sometimes, too much bacteria and phage result in the low titer. Solution: check your phage titer from ATTC, and using MOI around 0.1-1, Spotting assay first, double layer agar second, then using plate lysis to get high concentration of phage instead of mixing in culture sollution.

-Unsure what % agar to make the semisolid. 0.5-0.8% seems too runny, 1-1.2% could prevent the bacteria and phage from mixing. Each batch seems to come out differently as well. 

Normally I use soft agar from 0.5-0.7, it going well, you should keept your soft agar around 40-50 C, dont keep it to high before mixing with bacteria and phage (of course depending on bacterial features).

-How to spread the bacteria? Some procedures say to use a spreader, others say to add it to the semisolid before pouring that on the plate.

Yes, as quick as possible add bacteria, phage, mixing and pour it quickly to agar plate.

-Can dilutions of phage be stored overnight at 4°C and used again? Or will the phage decay?

Yes, of course. 

-Is it possible that ATCC sent us dud phage?

I dont know, you should consult them.

Troubles with Titer: How to get good plaques? - ResearchGate. Available from: https://www.researchgate.net/post/Troubles_with_Titer_How_to_get_good_plaques [accessed Mar 15, 2017].

first centrfuge the sample twice and mix with buffer gelatin .